Hello - I hope you can reassure me a bit! My 7 months old DS sits up without support even for a fairly long time, rolls over when he wants, and bears some weight on his legs. However, when on his tummy he just lifts his head very briefly then drops it, and sometimes he drops his head forwards when on the Jumparoo, and (although rarely) when on the highchair. It just looks as if his head feels too heavy and needs a rest. He's not a big fun of tummy time, but then again his big brother wasn't either and was a bottom shuffler (and so was I).
DS does have a massive head, almost off the scale. I wonder if this has got something to do with it. But it just looks strange!